The present invention relates to an apparatus and method for rapidly and accurately pinpointing the location of an underground leak in a gas line in a manner that greatly reduces the risks of explosion.
Determining the location of a leak in an underground gas line has long posed difficult problems for gas line emergency repair crews. Although the leaking gas line itself is easily located, the permeation of the soil or other overlayer with gas from the leak makes it difficult to pinpoint the actual location of the leak. As a result, it has not been uncommon for large stretches of a surface, including paved roadways, to have to be excavated in a somewhat random fashion to locate the actual site of the leak. This, of course, is costly and time-consuming. In addition, the continuous leaking gas creates a greater hazard the longer the leak continues.
It is known in the prior art to use a so-called “bar hole purger” to remove gas from a small hole drilled near the suspected point of the leak. A compressor/venturi arrangement is connected to the bar hole probe to draw gas from the bore hole and, after the probe is withdrawn, the time it takes for gas to return to the bore hole gives an indication of how close the hole is to the actual leak. This system is slow and costly, in terms of the amount of machinery required to locate the leak. In addition, the system has no safeguards to protect against a possible ignition of an explosive gas/air mixture.
In one recently developed apparatus, a vacuum suction head is placed over each of a series of boreholes drilled at spaced intervals along the length of a leaking gas line in the general area of the leak. Each of the suction heads is attached by a flexible hose to a manifold which, in turn, is attached to a truck-mounted industrial vacuum apparatus. A source of compressed air is also connected to the upstream end of the manifold. Simultaneously, compressed air is supplied at 100 psi and 160 cfm to the manifold and the vacuum apparatus is run at full capacity (e.g., 750 cfm) to the vacuum hopper. The combined airflow generated by the compressed air and the vacuum drawn by the vacuum apparatus draws gas in the underlying soil from the boreholes to the suction heads to rapidly evacuate gas in the areas of the boreholes. After gas is evacuated from the boreholes, the suction heads are removed and probes with gas sensors are inserted into the boreholes to measure gas levels. Because permeating gas will return more quickly to the boreholes closest to the leak, the position of the leak can be quickly determined. The initial readings of gas levels in the boreholes may also be used to reposition the suction heads, including drilling additional boreholes closer to the indicated position of the leak. The system is also used to generally evacuate gas that has permeated the soil around a leak in a gas line in order to minimize the toxic and explosive hazards to buildings and the like in the area.
The above described system suffers from a number of deficiencies. The system requires the infusion of substantial compressed air volumes into the evacuation line. The system is operated for a period of time (e.g., five minutes) estimated to be sufficient to evacuate gas from all the boreholes. Finally, the large vacuum hopper typically used with these vacuum systems provides a large volume that could potentially be the source of an explosive gas/air mixture, the ignition of which could be precipitated by a spark or static electric discharge.
The apparatus and method of the present invention address and correct the deficiencies in the prior art.